I accidentally clicked some shortcuts, and now my konsole screen is split.
I don't want it, how can I unsplit it?
Most likely you accidentally hit Ctrl+( (split view left/right) or Ctrl+) (split view top/bottom). To close views:
Ctrl+shift+x to close active view (default shortcut).
Ctrl+shift+o to close all but the current view (default shortcut).
More information is in the Konsole command reference.
In the menu "View", choose option "Split View", there "Close active view". It closes a split part inside the Konsole. Do it until you have only one.
If there is no menubar on the top of the Konsole window, then you can enable it in the popup menu by a right click (option "show menu list"). After it is visible, you can make it disappeared again in the "Settings" option.
The actual menu/option names were translated back to English, thus they may unexact. Anybody using an English KDE, feel free to fix it.